The present invention relates to low ignition propensity products and processes for making the same. Specifically, the present invention relates to products having one or more thermoplastic polymer aqueous suspension coated regions suitable for commercial use and methods of making such polymer suspensions printed products.
Low ignition propensity products are desired for safety as well as regulatory reasons. The term low ignition propensity products as used herein refers to such products having specific coated regions such that, if lit, and upon contacting a combustible substrate, for example, have a tendency to self extinguish themselves when the burning front reaches a coated region in the product unless actuated by other means, when, for example, air is drawn on by the user in connection with smoking cigarettes; or held in a free burn state in which the burning product is sufficiently exposed to the air on all of its sides.
As to cigarettes, conventional cigarette papers (also referred to as base papers) that are currently being used as cigarette wrappers have high ignition propensity. This is so because the natural porosities of these conventional cigarette papers are high, in the order of 20 to 120 Coresta porosities At these Coresta porosities, oxygen permeability is high. Cigarettes using such papers as wrappers when lighted have a tendency to burn their entire length and may ignite a flammable object if left on the object unattended Coresta porosity is a term commonly used in the industry and is expressed by the unit cc/minute/cm2 at 1 cbar pressure.
There have been various attempts, reported in the prior art, to modify the ignition propensity of the conventional cigarette papers. Some of these include polymer coatings particularly thermoplastic polymer coatings in the form of bands on the outer surface of the cigarette wrapper. However, these modified cigarette wrappers have various drawbacks.
For example, the thermoplastic polymers such as hydroxypropyl cellulose and ethyl cellulose have been applied to cigarette paper for the purpose of reducing cigarette burn rate. Although such wrappers can be used for making cigarettes with modified cigarette burn rate, these wrappers have organic solvent based polymer coatings not water based polymer coatings. Water based coatings have caused serious physical disruptions to the cigarette paper rendering it unusable for cigarette production. A justifiable interest exists in the cigarette industry to avoid organic solvent based polymers because such liquids or suspensions are not commercially feasible for use as an on-line process on the paper machine due to the problems of solvent fumes and fire hazards around paper machines and there is a significant risk of residual solvents remaining in the paper. Thus, use of organic solvents necessitates separate off-line printing process to make the modified cigarette paper. Other teachings disclose water dissolved hydroxypropyl cellulose coatings on the cigarette wrapper but they do not reduce the cigarette static burn rate.
Further, it has been reported that attempts to apply aqueous polymer solutions to the cigarette wrappers have been commercially unsuccessful because the aqueous solutions significantly reduce the strength of the paper, cause the paper to crinkle or pucker in the coated areas and the cigarettes made with these wrappers have a non-uniform and unappealing outer surface.
Thus, there is a need for use of products, including cigarettes having reduced burn rates and at the same time eliminating the reported problems of crinkling and puckering in the coated regions of the wrapper and/or paper.
The present invention provides products including cigarette papers containing a thermoplastic polymer aqueous suspension coated region(s) having reduced (Coresta) porosities suitable for making products with reduced burn rates. The invention uses high concentrations of thermoplastic polymer, enough to achieve sufficient paper porosity closure and hence cigarette burn rate retardation. The invention also provides ways to get sufficiently high enough concentrations of thermoplastic polymers into an aqueous vehicle at an low enough viscosity capable of being printed onto paper and/or wrappers via existing commercial printing techniques thus avoiding the cost of separate off-line converting processes and the problems of solvent fumes and fire hazards around paper machines.
The present invention also provides ways to eliminate the consequences due to the application of aqueous polymer solutions such as reducing the strength of the paper and also the paper crinkling or puckering in the coated areas.
In one aspect of the invention, a cigarette paper for making low ignition propensity cigarettes is provided. The cigarette paper has a base paper with a plurality of regions of thermoplastic polymer aqueous suspension printed on a surface of the paper. The aqueous suspension used as a printing ink does not have fibrous cellulose. The plurality of regions on the base paper have Coresta porosities of 0 to 14. The Coresta porosities of zero are achieved when all the pores in the coated region are sealed with the suspension. The cigarette paper also has a film of conditioning medium applied on to the surface containing the plurality of regions or on the opposite surface. The conditioning medium is water or water with a burning chemical. The thermoplastic polymer aqueous suspension has one or more thermoplastic polymers (such as hydroxypropyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, N-substituted acrylamides, poly(vinylmethylether), poly(ethylene oxide), poly(vinylalcohol) and poly(2-ethyl oxazoline), methyl cellulose ether, cellulose acetate, cellulose acetate phthalate, cellulose acetate butyrate) suspended in an aqueous medium but it has at least one thermoplastic polymer at concentrations greater than 10% w/w suspended in the aqueous medium. In one embodiment, the thermoplastic polymer aqueous suspension has ethyl cellulose at concentrations greater than 10% w/w suspended in the aqueous medium. In another embodiment, the thermoplastic polymer aqueous suspension has cellulose acetate phthalate at concentrations greater than 10% w/w suspended in the aqueous medium.
In another aspect of the invention a different type of cigarette paper for making low ignition propensity cigarettes is provided. The base paper here has a plurality of regions of hydroxypropyl cellulose aqueous suspension printed on a surface of the paper. The plurality of regions of the base paper have Coresta porosities from about 4 to about 10. The aqueous suspension has at least about 10% w/w hydroxypropyl cellulose. The aqueous suspension used as a printing ink does not have fibrous cellulose.
In still another aspect of the invention a different type of cigarette paper for making low ignition propensity cigarettes is provided. This cigarette paper has a base paper with a plurality of regions of thermoplastic polymer aqueous suspension printed on a surface of the paper. The aqueous suspension does not have fibrous cellulose but has only ethyl cellulose at a concentration of at least about 10% w/w and one other thermoplastic polymer (such as for example ethyl hydroxyethyl cellulose from about 0.3 to about 0.8% w/w). The plurality of regions on the base paper have Coresta porosities from about 1.5 to about 10.
In yet another aspect of the invention a different type of cigarette paper for making low ignition propensity cigarettes is provided. This cigarette paper has a base paper with a plurality of regions of thermoplastic polymer aqueous suspension printed on a surface of the paper and again the aqueous suspension does not have fibrous cellulose but has only cellulose acetate phthalate at a concentration of at least about 10% w/w and one other thermoplastic polymer and wherein the plurality of regions of the base paper have Coresta porosities from about 1.5 to about 10.
In a further aspect of the invention, a different type of cigarette paper is provided. This cigarette paper has a base paper with a plurality of regions of thermoplastic polymer, not of fibrous cellulose, aqueous suspension printed on a surface of the paper. The thermoplastic polymer aqueous suspension has one or more thermoplastic polymers suspended in an aqueous medium with at least one thermoplastic polymer at concentrations greater than 10% w/w suspended in the aqueous medium and wherein the plurality of regions of the base paper have Coresta porosities of 1 to 10. This cigarette paper also has a film of conditioning medium applied on to the surface containing the plurality of regions or the opposite surface thereof, wherein said conditioning medium is water or water with a burning chemical.
In a different aspect of the invention a composition for use as a printing ink to make low ignition propensity products comprising a thermoplastic polymer at concentrations from about 10% w/w to about 40% w/w suspended in an aqueous medium. The thermoplastic polymer is a cloud polymer or a room temperature polymer.
In another aspect of the invention a method for making a cigarette paper for low ignition propensity cigarettes with a plurality of regions of a thermoplastic polymer aqueous suspension printed on to a surface of a base paper is provided. The method includes the steps of advancing the base paper along a mechanical path so as to pass through a thermoplastic polymer aqueous suspension-printing station; and applying at said station, a thermoplastic polymer aqueous suspension to a surface of the base paper so as to form a plurality of regions containing said suspension. The plurality of regions on the base paper have Coresta porosities ranging from 0 to 14.9 or 0.1 to 14 or 0.5 to 10 or 1 to 10 or Coresta porosities ranging from about 1 to about 10. The method also includes an additional step of applying a uniform film of a conditioning medium to the surface of the base paper (or on the opposite side of the base paper) following the printing station application. The conditioning medium is water if the base paper used has a burning chemical or else the conditioning medium is water with a burning chemical. The thermoplastic polymer aqueous suspension-printing station is a heated or unheated size press rotogravure station.